Formation and Structure of Cross-Linked Polyacrylates (original) (raw)

Models developed to describe free radical crosslinking polymerizations may be divided into three classes: statistical models, kinetic descriptions, and kinetic gelation simulations. This paper provides a comparison of the three types of models by describing the approach, assumptions, strengths, and limitations of each when applied to lightly crosslinked systems. The greatest strength of the statistical approach arises from the wealth of post-gel structural information that can be obtained, however these models have difficulty accounting for history-dependent effects. Kinetic descriptions may properly describe history-dependent reaction non-idealities, but are unable to account for localized effects that are prevalent in highly crosslinked systems. The kinetic gelation simulations may describe topological constraints and localized effects but are of limited use for lightly crosslinked polymers due to their inability to accurately account for molecular motions. In recent years there has been considerable interest in water-swellable "superabsorbing" polymers capable of absorbing and holding large amounts of water. These polymers have found extensive commercial application as sorbents in personal care products such as infant diapers, feminine hygiene products, and incontinence products (7 ,2), and have received considerable attention for a variety of more specialized applications including matrices for enzyme immobilization (3), biosorbents in preparative chromatography (3), materials for agricultural mulches (4), and matrices for controlled release devices (5). The interest in superabsorbing polymers is illustrated by the popularity of the ACS symposium upon which this volume is based, as well as the recent proliferation of research articles on the topic (for reviews, see references 1-7).